Project Summary1. IKKalpha in lung squamous cell carcinoma development. Lung cancer is the leading cause of cancer mortality worldwide; however, there are no robust animal models of lung squamous cell carcinomas (SCCs), one of the major types of lung cancer. Here, we detected spontaneous lung SCCs in kinase-dead IKKalpha knock-in mice and markedly increased leukocytes, cytokines, and chemokines in the mutant lungs. We identified deregulated c-myc, Nanog, Oct3/4, p53, Rb, EGFR, MAPK, Jun-B, p63, Trim29, Rhov, CDK1, and IGF1 in mouse lung SCCs, and identified reduced IKKalpha and IkappaBalpha and increased ROS1 in mutant lungs and SCCs, some of which were found in human lung SCCs. Lung cancers were prevented by reintroducing epithelial-cell IKKalpha, depleting macrophages, or depleting lymphocytes; whereas mutant bone marrow reconstituted lung SCCs in irradiated mutants, suggesting that IKKalpha inactivation or inflammation is a driver. This study not only provides a novel model for studying the pathogenesis, treatment, early detection, and prevention of human lung SCCs, but also demonstrates how a single mutation in IKKalpha elicits malignancy through the combined epithelial-cell-autonomous and immune mechanisms. 2. IKKalpha regulates early B cell development. Multiple transcription factors regulate B cell commitment, which coordinates with myeloid-erythroid lineage differentiation. NF-kappaB has long been speculated to regulate early B cell development; however, this issue remains controversial. IKKalpha is required for splenic B cell maturation, but not for bone marrow (BM) B cell development. Here, we unexpectedly found defective BM B cell development and increased myeloid-erythroid lineages in kinase-dead IKKalpha (KA/KA) knock-in mice. Markedly increased cytosolic p100, an NF-kappaB2 inhibitory form, and reduced nuclear NF-kappaB p65, RelB, p50, and p52, as well as IKKalpha, were observed in KA/KA splenic and BM B cells. Several B- and myeloid-erythroid-cell regulators, including Pax5, were deregulated in KA/KA BM B cells. Using fetal liver and BM congenic transplants, and deleting IKKalpha from early hematopoietic cells in mice, this defect was identified as B cell intrinsic and as an early event during hematopoiesis. Reintroducing IKKalpha, Pax5, or combined NF-kappaB molecules promoted B cell development, but repressed myeloid-erythroid cell differentiation in KA/KA BM B cells. Together, these results demonstrate that IKKalpha regulates B-lineage commitment via combined canonical and noncanonical NF-kappaB transcriptional activities to target Pax5 expression during hematopoiesis. 3. IKKalpha is required for maintaining skin homeostasis and preventing skin tumorigenesis. However, its signaling has not been extensively investigated. In the present study, we generated two mouse lines that expressed different levels of transgenic IKKalpha in the basal epidermis under the control of the keratin 5 promoter and further evaluated their effects on the major pathways of inflammation, proliferation, and differentiation in the skin. Regardless of the transgenic IKKalpha levels, the mice develop normally. Because IKKalpha deletion in keratinocytes blocks terminal differentiation and induces epidermal hyperplasia and skin inflammation, we depleted the endogenous IKKalpha in these transgenic mice and found that the transgenic IKKalpha represses epidermal thickness and induces terminal differentiation in a dose-dependent manner. Also, transgenic IKKalpha was found to elevate expression of Max dimer protein 1 (Mad1) and Ovol1, c-Myc antagonists, but repress activities of EGFR, ERK, Jun-amino-terminal kinases, c-Jun, Stat3, and growth factor levels in a dose-dependent fashion in the skin. Moreover, EGFR reduction represses IKKalpha deletion-induced excessive ERK, Stat3 and c-Jun activities and skin inflammation. These new findings indicate that elevated IKKalpha expression not only represses epidermal thickness and induces terminal differentiation, but also suppresses skin inflammation by an integrated loop. Thus, IKKalpha maintains skin homeostasis through a broad range of signaling pathways.